godfrey he created FLINK-5406:
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Summary: add normalization phase for predicate logical plan
rewriting between decorrelate query phase and volcano optimization phase
Key: FLINK-5406
URL: https://issues.apache.org/jira/browse/FLINK-5406
Project: Flink
Issue Type: New Feature
Components: Table API & SQL
Reporter: godfrey he
Normalization phase is for predicate logical plan rewriting and is independent
of cost module. The rules in normalization phase do not need to repeatedly
applied to different logical plan which is different to volcano optimization
phase. And the benefit of normalization phase is to reduce the running time of
volcano planner.
`ReduceExpressionsRule` can apply various simplifying transformations on
RexNode trees. Currently, there are two transformations:
1) Constant reduction, which evaluates constant subtrees, replacing them with a
corresponding RexLiteral
2) Removal of redundant casts, which occurs when the argument into the cast is
the same as the type of the resulting cast expression
the above transformations do not depend on the cost module, so we can move the
rules in `ReduceExpressionsRule` from DATASET_OPT_RULES/DATASTREAM_OPT_RULES to
DataSet/DataStream Normalization Rules.
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